Method of manufacturing a zeolitic adsorbent useful for aromatic separation

ABSTRACT

A method of manufacturing a solid adsorbent which method comprises the steps of: contacting a base material containing type X or type Y zeolite with a fluoride-containing solution of sodium hydroxide at first ion exchange conditions to effect the addition of sodium cations to and the extraction of alumina from the base material; ion exchanging the base material at second ion exchange conditions to effect the essentially complete exchange of sodium cations; and, drying the exchanged zeolite at conditions ro reduce the LOI at 900*C. to less than about 10 wt. %. The sodium cations can be essentially completely exchanged with either barium and potassium cations in a weight ratio of from about 1.5 to 200 or with barium cations alone. The combination fluoride-caustic treatment prior to the exchange with potassium and barium or with barium alone produces a superior adsorbent for separating the para isomer from a feed mixture comprising at least two bi-alkyl substituted monocyclic aromatic isomers, including the para isomer, the isomers having from 8 to about 18 carbon atoms per molecule. The adsorbent so produced has faster para isomer transfer rates and higher aromatic capacity than one produced either from untreated base material or from base material treated with fluoride or caustic alone. Additionally a fluoride treatment of base material alone or in combination with or subsequent to a caustic treatment, prior to potassium and barium or barium ion exchange, essentially eliminates a troublesome dustiness characteristic of adsorbents prepared from untreated base material.

United States Patent 1191 Rosback 1451 Apr. 15, 1975 [54] METHOD OFMANUFACTURING A ZEOLITIC ADSORBENT USEFUL FOR AROMATIC SEPARATION DonaldH. Rosback, Elmhurst, Ill.

[73] Assignee: Universal Oil Products Company, Des Plaines, Ill.

[22] Filed: Sept. 28, 1973 [21] App]. No.: 401,783

Related U.S. Application Data [63] Continuation-in-part of Ser. No.356,666, May 2,

[75] Inventor:

Primary E.taminerC. Dees Attorney, Agent, or FirmJames R. Hoatson, Jr.;Thomas K. McBride; William H. Page, II

[5 7] ABSTRACT A method of manufacturing a solid adsorbent which methodcomprises the steps of: contacting a base material containing type X ortype Y zeolite with a fluoride-containing solution of sodium hydroxideat first ion exchange conditions to effect the addition of sodiumcations to and the extraction of alumina from the base material; ionexchanging the base material at second ion exchange conditions to effectthe essentially complete exchange of sodium cations; and, drying theexchanged zeolite at conditions ro reduce the LOl at 900C. to less thanabout 10 wt. The sodium cations can be essentially completely exchangedwith either barium and potassium cations in a weight ratio of from about1.5 to 200 or with barium cations alone.

The combination fluoride-caustic treatment prior to the exchange withpotassium and barium or with barium alone produces a superior adsorbentfor separating the para isomer from a feed mixture comprising at leasttwo bi-alkyl substituted monocyclic aromatic isomers, including the paraisomer, the isomers having from 8 to about 18 carbon atoms per molecule.The adsorbent so produced has faster para isomer transfer rates andhigher aromatic capacity than one produced either from untreated basematerial or from base material treated with fluoride or caustic alone.Additionally a fluoride treatment of base material alone or incombination with or subsequent to a caustic treatment, prior topotassium and barium or barium ion exchange, essentially eliminates atroublesome dustiness characteristic of adsorbents prepared fromuntreated base material.

14 Claims, No Drawings 1 METHOD OF MANUFACTURING A ZEOLITIC ADSORBENTUSEFUL FOR AROMATIC SEPARATION RELATED APPLICATIONS This application isa continuation-in-part application of copending application Ser. No.356,666. filed May 2, 1973 all the teachings of which copendingapplication are incorporated herein by specific reference thereto.

BACKGROUND OF THE INVENTION 1. Field of the Invention The field of artto which this invention pertains is crystalline aluminosilicateadsorbent production. More specifically, this invention relates to amethod of manufacturing an adsorbent having characteristics desirablefor the separation of certain aromatic isomers.

2. Description of the Prior Art There are numerous methods for themanufacture and ionexchange of various crystalline aluminosilicates,particularly the type X and type Y crystalline aluminosilicates, toyield products useful for effecting given hydrocarbon reactions orseparations. In the method of this invention, a manufacturing method hasbeen discovered whereby an adsorbent material is pro duced havingsuperior properties with respect to the separation of the para isomerfrom a feed mixture comprising at least two bi-alkyl substitutedmonocyclic aromatic isomers. including the para-isomer. the isomershaving from 8 to 18 carbon atoms per molecule.

A common problem encountered with most adsorbents and many catalysts isdust which can form excessive pressure drop after the adsorbent orcatalyst has been loaded into the adsorbent chambers or reaction vessel.Certainly it is for this reason that adsorbents and catalysts aremanufactured to meet certain minimum physical strength requirements andthat they are loaded into chambers and vessels with care to avoidbreakage. Although operations such as screening can be used to removemost of the interstitial smaller particles and dust such operationsgenerally fail to remove dust which may coat particles of adsorbent orcatalyst of the proper size. This type of dust, apparently held to theparticle by electrostatic attraction, may then later be removed byliquid passing through the adsorbent chamber or catalyst vessel andaccumulate to form excessive pressure drops.

I have discovered that the troublesome dustiness characteristic ofadsorbents is virtually eliminated by a fluoride treatment of the basematerial. It is thought that the fluoride solublizes the dust byreacting with combined aluminum compounds present in the dust therebyremoving the dust from the particles.

In the method of our invention I have additionally found that anion-exchange of a base material with a fluoride-containing aqueoussolution of sodium hydroxide followed by an ion-exchange with potassiumand barium or with barium alone and then a drying step produces andadsorbent with faster transfer rates and higher aromatic capacity thanadsorbents produced by either fluoride or caustic treatment alone orwith untreated base. Although it is hypothesized that the ionexchangewith aqueous sodium hydroxide replaces non-sodium cations such as H+ orGroup II-A cations occupying exchangeable sites within the zeolite andthereby permits higher amounts of barium and potassium or barium aloneto be added during a subsequent ion-exchange step. the synergisticresult obtained by combining the fluoride treatment with the sodiumionexchange is neither expected nor understood.

The prior art has neither disclosed nor suggested the method of ourinvention to produce these results.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a process for the manufacture of a zeolitic adsorbent whichprocess employs a type X or type Y structured zeolite as an intregalcomponent of the finished adsorbent. It is another object of the presentinvention to provide a new method for the manufacture of an adsorbentwhich has superior properties when used for the separation of paraaromatic isomers and in particular for the separation of para-xylene.

In brief summary, my invention is, in one embodiment, a method ofmanufacturing a solid adsorbent useful for the separation of thepara-isomer from a feed mixture comprising at least two bi-alkylsubstituted aromatic isomers. including the para-isomer. said isomershaving from 8 to about 18 carbon atoms per molecule which methodcomprises the steps of: (a) contacting a base material containing type Xor type Y zeolite with a fluoride-containing solution of sodiumhydroxide solution at first ion-exchange conditions to effect theaddition of sodium cations to and the extraction of alumina from thebase material; (b) ion-exchanging the base material at secondion-exchange conditions to effect the essentially complete exchange ofsodium cations; and, (c) drying the resulting exchanged mass atconditions to reduce the LOI at 900 C. to less than about 10 wt. 7:.

DESCRIPTION OF THE INVENTION The type X and type Y crystallinealuminosilicates or zeolites herein contemplated are described as athreedimensional network of fundamental structural units consisting ofsilicon-centered SiO and aluminumcentered AlO tetrahedra interconnectedby a mutual sharing of apical oxygen atoms. The space between thetetrahedra is occupied by water molecules and subsequent dehydration orpartial dehydration results in a crystal structure interlaced withchannels of molecular dimension.

where M represents at least one cation having a valence of not more than3, n represents the valence of M and y is a value up to about 8depending upon the identity of M and the degree of hydration of thecrystal. The cation M may be one or more of a number of cations such asthe hydrogen cation, the alkali metal cation, or

the alkaline earth cations or other selected cations and is generallyreferred to as an exchangeable site.

The type Y structured zeolite in the hydrated or partially hydrated formcan be represented in terms of the mole oxides for the sodium form asrepresented by Formula 2 below:

Formula 2 (0.9102)Na O:Al O :wSiO :yH O

where w is a value of greater than about 3 up to 8. and y may be anyvalue up to about 9.

The term type X zeolite and type Y zeolite" as employed herein shallrefer not only to type X structured and type Y structured zeolitescontaining sodium cations but to those containing other cations such asthe hydrogen cations. the alkali metal cations or the alkaline earthcations. Typically both the type X and type Y structured zeolites asinitially prepared are predominantly in the sodium form but they maycontain. possibly as impurities. the other cations as mentioned above.

The term base material as used herein shall refer to a type X or type Yzeolite-containing starting material used to make final adsorbent by themethod of this invention. Usually such base material will bepredominantly in the sodium form of the zeolite. Generally the basematerial will be in the form of particles such as extrudates,aggregates, tablets. pills. macro-spheres, or granules produced bygrinding any of the above to a desired size range. The type X or type Yzeolite can be present in the base material in concentrations generallyranging from about 75 wt. 7( to about 90 wt. 7: of the base materialbased on a volatile free composition. The remaining material in the basematerial generally comprises amorphous silica or alumina or both whichis present in intimate mixture with the zeolite material. This amorphousmaterial may be an adjunct of the manufacturing process of the type X ortype Y zeolite (for example. intentionally incomplete purification ofthe zeolite during its manufacture) or it may be added to the relativelypure zeolite to aid in forming particles of the zeolite.

A specific base material is commercially available nomi'nal l/l6-inchextrudate comprising 13X zeolite and a minor amount of amorphousmaterial as binder. This base material is primarily in the sodium form;that is, the cation represented as M in Formula 2 above is primarilysodium. By chemical analysis the Na OlAl O ratio is usually about 0.7 orless and can typically be about 0.6 or less which, it should be noted,is less than the 09:02 indicated in Formula 1 above. Other cations suchas H+ and any of the Group "A metal cations may be present. primarily asimpurities, to supply the remainder of the cations needed for chemicalbalance. The silica to alumina ratio of this starting material by X-raydetermination is about 2.5 and the same ratio by chemical analysis isabout 2.6. Normally the starting material whether in the extrudate orpellet form is granulated to a particle size range of about -40 mesh(Standard U.S. Mesh) before the first ion exchange step is begun. Thisis approximately the desired particle size of the finished adsorbent.

The first ion exchange with a fluoride-containing sodium hydroxidesolution replaces non-sodium cation impurities in the type X or type Yzeolite contained in the base material thereby converting the zeoliteessentially completely to the sodium form. Increasing the sodium contentof the. zeolite permits a higher loading of barium and potassium cationsor of the barium cation alone into the zeolite structure on a subsequention exchange. To produce an acceptable adsorbent it is preferred thatthe sodium content of the starting material. as characterized by theweight ratio Nago/Algog be increased to a ratio greater than about 0.70and more preferably from about 0.75 to L0. [on exchange conditionsshould be so regulated to achieve this degree of ion exchange.

Although mild ion exchange conditions are employed. this stepadditionally removes a small amount of silica and alumina. Total silicaand alumina removal from the base material is from about l to about 15%and is generally in the range of about 1 to 5 wt. 7:. Analyses indicatethat the bulk of both soluble and insoluble material removed from thebase material is aluminum, as alumina or sodium aluminate. At least aportion of the alumina extracted appears to be from the zeolite itselfrather than from any amorphous material since there is some nominal lossof zeolite as detected by X-ray analysis after this step. It is notknown whether the small amount of silica removed from the base materialcame from the crystalline (zeolite) portion or the amorphous portion ofthe base material.

The degree of ion exchange and extraction of alumina achieved is afunction of the three variables of caustic and fluoride concentrations.temperature at which the ion exchange is conducted, and the length oftime the ion exchange is continued.

The preferred fluoride-containing sodium hydroxide solution employedwill be sodium hydroxide and sodium fluoride dissolved in water.Suitable concentrations to obtain the desired ion exchange can be fromabout 0.5 to 10 wt. 7: of sodium hydroxide with the preferredconcentration being from about 0.5 to 5 wt. "/1 and from about 0.1 wt.7: up to the solubility limit (about 5%) of sodium fluoride. By usingsolutions containing sodium hydroxide and sodium fluoride within theseranges of concentration. the desired ion exchange can be obtained attemperatures from about 50 to 250 F. with temperatures from about 150 to250 F. being especially preferred. Operating pressure is not criticaland need only be sufficient to insure a liquid phase. Operatingpressures can range from about atmospheric pressure to about psig. Thelength of time required for the ion exchange will vary, depending uponthe solution concentration and temperature, from about 0.5 to 5 hours.Within the above preferred concentrations and temperature ranges, acontact time which has been shown to be especially preferred is about 2to 3 hours. Continuous or batch-type operations can be employed. The ionexchange step should be controlled so that the zeolite structure willnot be destroyed and so that the final product will have a Nap/A1 0ratio greater than about 0.7.

After the first ion exchange step the sodium exchanged particles aretreated at second ion-exchange conditions to effect essentially completeexchange of the sodium cations with both barium and potassium cations ina weight ratio of from about 1.5 to 200 or with barium cations alone.

Second ion exchange conditions will include a temperature of from about50 F to about 250F. and a pH sufficient to preclude the formation of thehydrogen form of the zeolite. The pH will therefore be greater than 7and preferably within the range of 7 to l0. Operation pressure is notcritical and need only be sufficient to insure a liquid phase. Operatingpressures can range from about atmospheric pressure to about 150 psig.The length of time for the essentially complete exchange of the sodiumcations will be from about 0.5 to about 5 hours depending upon theconcentration of the cation in the ion exchange medium and thetemperature. The term essentially complete exchange" as used hereinshall mean that the sodium cation content has been reduced to about 2.0wt. 7: or less and more preferably to about 1 wt. 7( or less.

The preferred method of ion-exchange when the adsorbent contains bothbarium and potassium cations is a two-step procedure wherein thesodium-exchanged particles are intially treated in contact with anaqueous solution of a potassium salt. preferably an aqueous solution ofpotassium chloride, for a time sufficient to reduce the sodium cationsto less than about 2 wt. of the zeolite and yield the potassium form ofthe zeolite. The exchange can be either a continuous or a batch typeoperation. The ion-exchange is suitably accomplished on passing a 7 wt.7( aqueous potassium chloride solution through a bed of thesodium-exchanged particles at about 180 F. at a liquid hourly spacevelocity of about one until a total of approximately 13 pounds ofsolution per pound of said particles has been passed in contacttherewith.

The potassium-exchanged particles can then be washed with water toremove excess ion exchange solution.

The washing medium will be water which has a pH adjusted to andmaintained within the range of 7 to by adding small amounts of potassiumhydroxide. Since the primary purpose of the sodium cation ion exchangewas to remove hydrogen cation (and metal cation) contaminants, this pHrange is necessary to avoid redepositing hydrogen cation on theadsorbent mass. Washing temperatures can include temperatures within therange of about 100 F. to about 200 F. with a temperature of about 100 F.to 145 F. preferred. Although the washing step can be done in a batchmanner with one aliquot of wash water at a time, the washing step isgenerally and preferably done on a continuous flow type basis with waterpassed through a bed of the adsorbent at a given liquid hourly spacevelocity and a temperature for a period of time in order than from about1 to about 5 gallons of water per pound of starting material is used towash the material. Preferred washing conditions include using liquidhourly space velocities from about 0.5 to 5. with [.5 being preferred,to pass from about 1 to about 3 gallons of wash water per pound ofstarting material over the ion exchanged adsorbent.

The potassium-exchanged particles arethen treated in contact with anaqueous solution of a barium salt in the second step of the two-stepion-exchange procedure to achieve the desired weight ratio of barium topotassium on the finished adsorbent. Preferably an aqueous solution offrom about 0.2 to about 5 wt. 7: barium chloride is recycled through theparticle bed at about 180F, and at a liquid hourly space velocity offrom about I to about 5 until the-desired degree of exchange has beenachieved. After the barium-exchange step is completed, the water-washingstep is repeated,

again maintaining a pH of 7 or greater in order to prevent or minimizethe possibility of formation of the hydrogen form of the zeolite. A goodindication of complete washing can be made by quantitatively testing theeffluent wash water for the presence of the anion portion of the saltused in the ion exchange solution.

The above-mentioned two-step potassium and barium ion-exchange procedureis not necessarily limiting as it has been found possibly to employ asingle step ion-exchange in which both barium and potassium are placedon the zeolite. However, the two-step procedure allows more precisecontrol of the amount of cations placed on the zeolite.

When it is desired that the sodium cations be essentially completelyexchanged with only barium cations then a procedure like that of thesecond step of the above described two-step procedure will be used aloneto effect the exchange with barium cations. l have found that by themethod of this invention a suitable adsorbent can be prepared withoutthe potassium catlOnS.

When the wash step is completed the wet adsorbent particles will usuallycontain from about 30 to about 50 wt. 7: volatile matter (water) asmeasured by loss on ignition to 900 C. [n this specification, thevolatile matter content of the zeolitic adsorbent is determined by theweight difference obtained before and after drying a sample of adsorbentin a high temperature furnace at 900 C. under an inert purge gas streamsuch as nitrogen for a period of time sufficient to achieve a constantweight. The difference in weight, calculated as a percentage of thesample's initial weight. is reported as loss on ignition (LOl) at 900 C.and represents the volatile matter present within the adsorbent. Theremaining step in the method of manufacture then is the drying step toreduce the LO] at 900 C. to less than about 10 wt. 7: with the preferredLOl being about 3 to 7 wt. /1. After the washing has been completed, theparticles can be unloaded and dried in a force air oven at temperaturesabove the boiling point of water but less than about 500 C. andpreferably about C., for a period of time sufficient to remove enoughwater so that the volatile matter content of the zeolite is below about10 wt. "/1. Other methods of drying may be used which can include dryingin the presence of an inert gas or under a vacuum. or both.

The anticipated use for the adsorbent prepared by the method of thisinvention is in various processes for the separation of the para isomerfrom a feed mixture comprising at least two-bialkyl substitutedmonocyclic aromatic isomers, including the paraisomer, said isomerhaving from 8 to about 18 carbon atoms per molecule. Specifically, ouradsorbent is useful for separating the para-xylene from a feed mixturecomprising paraxylene and at least one other C aromatic isomer.

-The particular usefulness of this adsorbent and general insight intoits desirable characteristics may be better understood by briefreference to such aromatic isomers and separation processes.Specifically, the feed stocks which can be used in the process of thisinvention are characterized by the formula shown in Formula 3 below:

Formula 3 Wherein, R,, R R and R are selected from the group of alkylchains in a manner to allow an essentially bialkyl substitution ateither ortho-, meta-. or paraisomer positions. The R substitutionalgroups can inelude alkyl groups ranging from methyl substitution groupsup to and including chains having 1 l or less carbon atoms per molecule.The alkyl side chains can be both normal and branched in nature and arepreferably saturated chains.

Specific representative compounds which can be utilized as feedstocks inthe process include those feedstocks containing the xylene isomers andethylbenzene and the various isomers of methylethylbenzene.diethylbenzene. isopropyltoluene, the methylpropylbenzenes.ethylpropylbenzenes. methylbutylbenzenes. ethylbutylbenzene,dipropylbenzenes, methylpentylbenzene. etc.. and combinations thereof.The above list only represents a small fraction of compounds whoseisomers can be separated by the specific adsorbent produced by themethod of this invention.

The isomers of such compounds are separated by this adsorbent accordingto their configuration depending whether they are of a para-. metaorortho-isomer construction. Specifically. the para isomer is selectivelyadsorbed relative to the other isomers. It is contemplated that withfeed stocks containing mixtures of more than one class of isomers. forexample. C isomers in mixture with C or C isomers. molecular weightdifferences will unduly interfere with selective adsorption based uponisomer configuration differences. It is therefore preferred that theprocess utilizing the adsorbent produced by the method of this inventionto employ feed stocks comprising only a single class of aromaticisomers, that is, aromatic isomers having an equal number of carbonnumber per molecule. It is more preferable to use isomers having astheir only differences the location of the alkyl substituted groups in apara-, metaor ortho-position. The alkyl structures should preferably bethe same for each isomer of a class. In some instances an isomer mayhave alkyl chains which are both normal or branched or one branched andone normal.

The feed stocks may contain small quantities of straight or branchedchain paraffins. cyclo-paraffins or olefinic material. It is preferableto have these quantities at a minimum amount in order to preventcontamination of products from this process by materials which are notselectively adsorbed or separated by the adsorbent. Preferably theabove-mentioned contaminants should be less than about of the volumefeed stock passed into the process.

To separate the para isomer contained in the feed mixture, the feed iscontacted with a bed or beds of the structured zeolite adsorbent and thepara isomer is selectively retained by the adsorbent while theunadsorbed or raffinate mixture which comprises the other isomers isremoved from the interstitial void spaces between the particles oradsorbent and the surface of the adsorbent. The adsorbent is thencontacted with a desorbent material which is capable of displacing theadsorbed para isomer from the adsorbent.

The adsorbent can be contained in a single chamber where throughprogrammed flow into and out of the chamber separation of the paraisomer is effected. A particularly preferred process to use theadsorbent of our invention employs the simulated moving-bedcountercurrent operations similar to those disclosed in the pattern ofoperations in US. Pat. No. 2,985,589. The preferred process forseparating the para isomer from a feed mixture containing at least twobi-alkyl substituted monocyclic aromatic isomers, including theparaisomer, said isomers having from 8 to about 18 carbon atoms permolecule would comprise the steps of: contacting the feed mixture withthe adsorbent at adsorption conditions to effect the selectiveadsorption of para-isomer by the adsorbent. withdrawing from the bed ofadsorbent a rafflnate stream comprising less selectively adsorbedaromatic isomers, contacting the adsorbent with a desorbent material atdesorption conditions to effect desorption of para isomer from theadsorbent. and withdrawing a stream containing the para isomer anddesorbent from the adsorbent.

Preferred operating conditions for both adsorption and desorption ofthis particular process include a temperature within the range of fromabout F. to about 450 F. and a pressure within the range of from aboutatmospheric to about 500 psig. Furthermore. both adsorption anddesorption of the para isomer are affected at conditions selected tomaintain liquid phase throughout the bed of adsorbent.

The adsorbent produced by the method of this invention may, of course,be used in other selective adsorption processes for separating aromaticisomers. These might include, for instance, swing-bed or moving-bedprocesses. Adsorption and desorption in such proceses may both beconducted in the vapor phase or liquid phase or one operation may beconducted in the vapor phase and the other in the liquid phase.Operating pressures and temperatures for adsorption and desorption mightbe the same or different.

The desorbents which can be used in the processes .employing thisadsorbent will vary depending on the generally operated at substantiallyconstant pressures and temperatures, the desorbent relied upon must bejudiciously selected in order that it may displace the adsorbed isomerfrom the adsorbent without unduly preventing the adsorbed isomer fromdisplacing the desorbent in a following adsorption cycle.

Desorbents which can be used in the process of this invention shouldalso be materials that are easily separable from the feed mixture thatis passed into the process. In desorbing the preferentially adsorbedcomponent of the feed both desorbent and the desorbed feed component areremoved from the adsorbent in admixture. Without a method of separationin these two materials, the purity of the selectively adsorbed componentof the feed stock would not be very high since it would be dilutedwith'desorbent. It is contemplated that a desorbent having a'differentboiling range than the feed mixture used should be used in this process.The use of a desorbent of a different boiling range allows a simpleseparation by fractionation or other methods to remove desired feedcomponents from the desorbent and allow reuse of the desorbent in theprocess. Specific desorbents which can be used in the process of thisinvention include benzene, toluene. esters. alcohols. cyclic dienes. theketones or a feed component material which has a significantly differentboiling range than a boiling range of the feed stock used. It iscontemplated that desorbents having both higher and lower boiling pointsin the feed stock can be utilized. Gaseous materials such as nitrogen,hydrogen. methane. ethane. etc.. can also be used as a desorbentmaterials where the desorbent operation takes place by a purging step.

With the type of processes employing adsorbent to separate aromaticisomers now in mind, one can appreciate that certain characteristics ofadsorbents are highly desirable. if not absolutely necessary, to thesuccessful operation of the selective adsorptive process. Among suchcharacteristics are: adsorptive capacity for some volume of the paraisomer per volume of adsorbent; adsorption for the para isomer withrespect to the other aromatic isomers and the desorbent; andsufficiently fast rates of adsorption and desorption of the para isomerto and from the adsorbent. Low or no initial dustiness of the adsorbentand attrition resistance are equally important to avoid possiblepressure drop problems after the adsorbent has been loaded.

Capacity of the adsorbent for adsorbing a specific volume of para isomeris of course a necessity; without such capacity the adsorbent is uselessfor adsorptive separation. Furthermore. the higher the adsorbentscapacity for the species to be adsorbed. the better is the adsorbent.The increased aromatic capacity of the particular adsorbent produced bythe method of this invention makes it possible to reduce the amount ofadsorbent needed to separate the desired species contained in aparticular rate of hydrocarbon feed mixture. A reduction in the amountof adsorbent required for a specific adsorptive separation reduces thecost of the separation process. It is, of course, important that thegood initial capacity of the adsorbent be maintained during actual usein the separation process over some economically desirable life.

The other important adsorbent characteristic is the ability of theadsorbent to separate components of the feed; or. in other words. theselectivity (B), of the adsorbent for one component as compared toanother component. Selectivity can be expressed not only for the desiredaromatic isomer (para isomer) as compared to undesired isomers but canalso be expressed between any feed stream isomer and the desorbent. Theselectivity (B) as used throughout this specification is defined as theratio of the two components of the adsorbed phase over the ratio of thesame two components in the unadsorbed phase at equilibrium conditions.

Selectivity is shown as Equation 1 below:

Equation 1 [voLpercent C/vol. percent DIA where C and D are twocomponents of the feed represented in volume percent and the subscriptsA and U represent the adsorbed and unadsorbed phases respectively. Theequilibrium conditions as defined here were determined when the feedpassing over a bed of adsorbent did not change composition aftercontacting the bed of adsorbent. In other words. there was no nettransfer of material occurring between the unadsorbed and adsorbedphases.

As can be seen where the selectivity of two components approaches l.0there is no preferential adsorption of one component by the adsorbent.As the (B) becomes less than or greater than 1.0 there is a preferentialselectivity by the adsorbent of one component. When comparing theselectivity by the adsorbent of one component C over component D, a (B)larger than 1.0 indicates preferential adsorption of component C withinthe adsorbent. A (B) less than 1.0 would indicate that component D ispreferentially adsorbed leaving an unadsorbed phase richer in componentC and an adsorbed phase richer in component D. Desorbents ideally wouldhave a selectivity equal to about 1 or slightly less than I.

The third important characteristic is the rate of exchange of theadsorbed para-isomer with the desorbentor. in other words. the relativerate of desorption of the para-isomer. This characteristic relatesdirectly to the amount of desorbent that must be employed in the processto recover the adsorbed isomer from the adsorbent. The adsorbentproduced by the method of this invention not only has higher aromaticcapacity and good selectivity but has faster transfer rates.

The remaining important characteristic. not only for adsorbents but forcatalysts as well. is low initial dustiness. This characteristic must ofcourse be coupled with sufficient particle mechanical strength to resistsubsequent dust formation during process usage. Such dust. whetherpresent initially or developed later. may migrate within the adsorbentchamber or reaction vessel during process use to form flow restrictionsfrom which excessive pressure drops can result. Such pressure dropsgrind up adsorbent or catalyst present in the chamber or vessel and canexceed equipment mechanical limitations thereby forcing prematureprocess shutdowns. We have discovered that the dustiness characteristicof adsorbents can be eliminated by a fluoride treatment step in themanufacture of such adsorbents. We would expect that such a step couldbe incorporated in catalyst manufacturing procedures as well as toeliminate the dustiness characteristic of any such catalyst.

In order to test various adsorbents to measure the characteristics ofadsorptive capacity. selectivity. and the rate of desorption, a dynamictesting apparatus is employed. The apparatus consists of an adsorbentchamber of approximately cc volume having inlet and outlet portions atopposite ends of the chamber. The chamber is contained within atemperature control means and, in addition. pressure control equipmentis used to operate the chamber at a constant predetermined pressure.Attached to the outlet line of the chamber is chromatographic analysisequipment used to analyze the effluent stream leaving the adsorbentchamber.

A pulse test. performed using this apparatus and the following generalprocedure. is used to determine selectivities and other data for variousadsorbent systems. The adsorbent was filled to equilibrium with aparticular desorbent by passing the desorbent through the adsorbentchamber. At a convenient time. a pulse of feed containing knownconcentrations of a nonadsorbed paraffmic tracer (n-nonane) and ofaromatic isomers all diluted in desorbent is injected for a duration ofseveral minutes. Desorbent flow is resumed, and the tracer and thearomatic isomers are eluted as in a liquid-solid chromatographicoperation. The effluent is analyzed by on-stream chromatographicequipment and traces of the envelopes of corresponding component peaksare developed.

From information derived from the chromatographic traces adsorbentperformance can be rated in terms of capacity index for the para isomer.selectivity for the para isomer with respect to the other isomers andrate of desorption of the para isomer by the desorbent. The capacityindex is characterized by the distance between the center of the paraisomer peak envelope and the C 7 tracer peak envelope. It is expressedin terms of the volume in cubic centimeters of desorbent pumped duringthis time interval. Selectivity. (B). for paraisomer with respect to theother isomers (p/m. p/o) is characterized by the ratio of the distancebetween the center of the para isomer peak envelope and the C tracerpeak envelope to the corresponding distances for the other isomers. Thetransfer rates are. we have found. best characterized by the widths ofthe tracer peak envelopes at half intensity. The narrower the peakwidths the faster the transfer rates.

In addition to the para isomer retention volume derived from the pulsetest total aromatic capacity is also obtained by measuring the volume ofa particular para isomer adsorbed per 70 cc of adsorbent. In this testthe adsorbent is first loaded to equilibrium with a feed blend of knownconcentrations of aromatic isomers and a tracer component. These arethen displaced with a desorbent containing a different para isomer thanthat of the feed. The amount of the latter para isomer adsorbed istermed the total aromatic capacity.

A comparison of the dust content in adsorbents can be made by simplypouring 10 ml. of the adsorbent into ml. of methanol contained in a 25 X95 mm 8 dram vial and mixing the contents. The dust will be dispersed inthe alcohol and the degree of opacity will serve as an index of the dustcontent.

To translate pulse test data and total aromatic capacity data into apractical aromatic separation process requires actual testing of thebest system in a continuous countercurrent liquidsolid contactingdevice.

The general operating principles of such a devise have been previouslydescribed and are found in Broughton U.S. Pat. No. 2,985,589 and aspecific laboratory-size apparatus utilizing these principles isdescribed in deRoset. et al., U.S. Pat. No. 3,706,812. The equipmentcomprises multiple adsorbent beds with a number of access lines attachedto distributors within the beds and terminating at a rotary distributingvalve. At a given valve position, feed and desorbent are beingintroduced through two of the lines and raffinate and extract arewithdrawn through two more. All remaining access lines are inactive andwhen the position of the distributing valve is advanced by one index allactive positions will be advanced by one bed. This simulates a conditionin which the adsorbent physically moves in a direction countercurrent tothe liquid flow. Additional details on adsorbent testing and evaluationmay be found in the paper Separation of C, Aromatics by Adsorption" byA. J. deRosset, R. W. Neuzil, A. J. Korous and D. H. Rosback presentedat the American Chemical Society, Los Angeles. Calif. Mar. 28-Apr. 2,

The superior performance of the adsorbents prepared by the method ofthis invention which was indicated by the pulse test was confirmed bycontinuous testing in this device.

EXAMPLE In this example four adsorbents were prepared from the same basematerial and tested to illustrate the desired properties achieved by themethod of this invention.

The four adsorbents were prepared from base material comprisingcommercially available 13X zeolite in the form of nominal l/16 X/za-inch extrudate. This base material was ground to produce 20-40 U.S.Standard Mesh particle size material and divided into four portions fromwhich four adsorbents were prepared.

One portion was simply barium exchanged to produce Adsorbent A. A 190 ccportion of the base material was treated upflow with 28 liters of 0.015BaCl. ,-2- H O solution at C. and 1.8 liquid hourly space velocity(LHSV). The material was then washed at 70 C. with 2 liters of waterover a 2.5 hour period.

A second portion was treated with a solution of NaF only and then bariumexchanged to produce Adsorbent B. A 300 cc portion of the base materialwas batch treated for 3.5 hours at 90 C. with 30 g. NaF dissolved in 600ml. of deionized water. The material was decantwashed and then bariumexchanged in the manner of Adsorbent A.

A third portion was treated with a solution containing both NaF and NaOHand then barium exchanged to produce Adsorbent C. A 200 cc portion ofthe base material was batch treated for 2 hours at 90 C. with a solutionof 25 g. NaF and 20 g. NaOH dissolved in 500 ml. of deionized water. Thematerial was batch washed at -85 C. for /2 hour periods with eight 250ml. portions of deionized water and then barium exchanged in the mannerdescribed above.

The fourth portion of ground base material was treated with a solutionof NaOH only and then barium exchanged to produce Adsorbent D. A 200 ml.portion of the base material was batch treated for 2 hours at C. with asolution of 20 g. NaOH dissolved in 500 ml. of deionized water. Thematerial was batch washed with water and then barium exchanged.

All four adsorbents were dried for 16 hours at 185 C. with perfluent Nand then rehydrated to 4 wt. 7: water prior to being tested forperformance by the pulse test previously described.

The testing apparatus was maintained at a controlled temperature of C.with sufficient pressure to ensure liquid phase operations. A desorbentof 30 vol. 7: para-diethylbenzene and 70 vol. 7c n-heptane was runthrough the apparatus at a rate of 1.5 cc per minute. At a convenienttime interval the desorbent was stopped and a feed pulse consisting of 5vol. 7: para-xylene, metaxylene. ortho-xylene, ethyl benzene, andn-nonane as a tracer and 75 vol. 7: desorbent was charged to theadsorbent chamber for a ten-minute interval at 1 LHSV.

From the chromatographic tracers of the envelopes of component peaks.peak envelope widths. paraxylene capacity. and selectivities weredetermined.

The amount of para-diethylbenzene adsorbed was determined by loading theadsorbent to equilibrium with a feed pulse consisting of 24 vol. 7! eachof the C aromatics and 4 vol. 7: n-nonane tracer and then charging thedesorbent of 30 vol. "/1 para-diethylbenzene and 70 vol. n-heptane tothe adsorbent chamber. The amount of para-diethylbenzene adsorbed wasthen calculated from the breakthrough front of paradiethylbenzenemeasured from the disappearance of the tracer.

Dust condition of the four adsorbents was'determined by the degree ofopacity resulting from the simple methanol test previously described.

The results of the testing for the four adsorbents are shown in table lbelow.

c. drying the thus exchanged base material at conditions to reduce theL01 at 900C. to less than about 2. The method of claim 1 furthercharacterized in that said base material has a Na O/Al O ratio of about0.7 or less.

3. The method of claim 1 further characterized in thatsaid solutioncontains sodium fluoride in a concentration of less than its solubilitylimit and sodium hydroxide in a concentration of from about 0.5 to about4. The method of claim 1 further characterized in that said first ionexchange conditions include a temperature within the range of from about50 F. to about 250 F.

5. The method of claim 1 further characterized in that said sodiumexchanged base material has a M 0- /Al O., ratio greater than about 0.7.

Table 1 Pulse Test and Capacity Data for Adsorbents Adsorbent A B C DTreatment none NaF NaF/NaOH NaOH Wt. "/1 BaO 30.4 31.4 35.6 32.6 Wt. Na1.40 1.74 1.02 1.05 Peak Envelope Widths. cc. for:

n-nonane 14.5 10.1 9.9 11.5

ethylbcnzene (EB) 20.4 15.4 15.0 19.2

para-xylene (P) 22.1 13.9 13.2 18.7

meta-xylene (M) 16.8 13.2 13.5 15.7

ortho-xylene (O) 16.8 12.6 13.5 15.5 Para-xylene retention volume. cc.19.6 23.0 23.5 24.8 selectivities P/EB 1.71 1.68 1.73 1.91

P/O 2.81 3.27 3.19 4.42 Para-dicthylbenzene capacity. cc.

per 70 cc adsorbent 6.38 8.00 9.75 9.15 Dust Condition dusty no dust nodust dusty The higher para-diethylbenzene capacities for Adsorbents Cand D indicate that both NaOH/NaF or NaOH treatments confer high totalaromatics capacity. The narrowest peak envelope widths for Adsorbent Cindicates that the NaOH/NaF treatment confers the fastest para-xylenetransfer rates. The table also shows that the best selectivities wereobtained with the NaOH treatment alone (Adsorbent D) with next bestselectivities obtained with the NaOH/NaF treatment (Adsorbent C).Additionally the table shows that NaF treatment with or without NaOHtreatment eliminates dusting (Adsorbents B and C).

The combination of NaOH and NaF treatment renders an adsorbent havingthe best combination of performance characteristics. This combination isnot attainable by either treatment alone and is certainly superior tothose of an adsorbent made with neither treatment.

1 claim as my invention:

1. A method of manufacturing a solid adsorbent comprising the steps of:

a. contacting a base material comprising X or Y zeolite with afluoride-containing aqueous solution of sodium hydroxide at first ionexchange conditions to effect the addition of sodium cations to and theextraction of alumina from said base material;

b. treating the sodium-exchanged base material at second ion exchangeconditions to effect the essentially complete exchange of sodium cationswith barium or barium and potassium cations; and.

6. The method of claim 1 further characterized in that said second ionexchange conditions include a pH sufficient to preculde formation of thehydrogen form of the zeolite. and a temperature within the range of fromabout F. to about 250 F.

7. The method of claim 1 further characterized in that saidsodium-exchanged base material is essentially completely exchanged withbarium and potassium cations.

8. The method of claim 7 further characterized in that the weight ratioof barium over potassium cations is from about 1.5 to 200.

9. The method of claim 1 further characterized in that saidsodium-exchanged base material is essentially completely exchanged withbarium cations.

10. A method of manufacturing a solid adsorbent which comprises thesteps of:

a. contacting a base material comprising a X or Y structured zeolitehaving a Nap/A1 0 ratio of about 0.7 or less with a fluoride-containingaqueous sodium hydroxide solution at first ion exchange conditions toincrease the sodium cation content of said mass to a Nap/A1 0 ratio ofgreater than about 0.7 and extract less than about 5% of the aluminafrom said base material;

b. treating the sodium-exchanged base material at second ion exchangeconditions, including a pH sufficient to preclude the formation of thehydrogen form of the zeolite and a temperature within the range of fromabout 50F. to about 250F., to effect the essentially complete exchangeof sodium cations with barium or barium and potassium cations; and.

c. drying the thus re-exchanged base material at conditions sufficientto reduce the LO] at 900C. to less than about lOwtf/r.

11. The method of claim 10 further characterized in that said solutioncontains sodium fluoride in a concentration less than its solubilitylimit and sodium-hydroxide in a concentration of from about 0.5 to about10 wt. 7?.

12. The method of claim 10 further characterized in that saidsodium-exchanged base material is essentially completely exchanged withbarium and potassium cations in a weight ratio of from about 1.5 to 200.

13. The method of claim 10 further characterized in reduce the 1.01 at900C. to less than about 10 wt. 7?.

1. A METHOD OF MANUFACTURING A SOLID ADSORBENT COMPRISING THE STEPS OF:A. CONTACTING A BASE MATERIAL COMPRISING X OR Y ZEOLITE WITH AFLUORIDE-CONTAINING AQUEOUS SOLUTION OF SODIUM HYDROXIDE AT FIRST IONEXCHANGE CONDITIONS TO EFFECT THE ADDITION OF SODIUM CATIONS TO AND THEEXTRACTION OF ALUMINA FROM SAID BASE MATERIAL; B. TREATING THESODIUM-EXCHANGED BASE MATERIAL AT SECOND ION EXCHANGE CONDITIONS TOEFFECT THE ESSENTIALLY COMPLETE EXCHANGE OF SODIUM CATIONS WITH BARIUMOR BARIUM AND POTASSIUM CATIONS; AND, C. DRYING THE THUS EXCHANGED BASEMATERIAL AT CONDITIONS TO REDUCE THE LOI AT 900*C. TO LESS THAN ABOUT 10WT. %.
 2. The method of claim 1 further characterized in that said basematerial has a Na2O/Al2O3 ratio of about 0.7 or less.
 3. The method ofclaim 1 further characterized in that said solution contains sodiumfluoride in a concentration of less than its solubility limit and sodiumhydroxide in a concentration of from about 0.5 to about 10 wt. %.
 4. Themethod of claim 1 further characterized in that said first ion exchangeconditions include a temperature within the range of from about 50* F.to about 250* F.
 5. The method of claim 1 further characterized in thatsaid sodium exchanged base material has a Na2O/Al2O3 ratio greater thanabout 0.7.
 6. The method of claim 1 further characterized in that saidsecond ion exchange conditions include a pH sufficient to preculdeformation of the hydrogen form of the zeolite, and a temperature withinthe range of fRom about 50* F. to about 250* F.
 7. The method of claim 1further characterized in that said sodium-exchanged base material isessentially completely exchanged with barium and potassium cations. 8.The method of claim 7 further characterized in that the weight ratio ofbarium over potassium cations is from about 1.5 to
 200. 9. The method ofclaim 1 further characterized in that said sodium-exchanged basematerial is essentially completely exchanged with barium cations.
 10. Amethod of manufacturing a solid adsorbent which comprises the steps of:a. contacting a base material comprising a X or Y structured zeolitehaving a Na2O/Al2O3 ratio of about 0.7 or less with afluoride-containing aqueous sodium hydroxide solution at first ionexchange conditions to increase the sodium cation content of said massto a Na2O/Al2O3 ratio of greater than about 0.7 and extract less thanabout 5% of the alumina from said base material; b. treating thesodium-exchanged base material at second ion exchange conditions,including a pH sufficient to preclude the formation of the hydrogen formof the zeolite and a temperature within the range of from about 50*F. toabout 250*F., to effect the essentially complete exchange of sodiumcations with barium or barium and potassium cations; and, c. drying thethus re-exchanged base material at conditions sufficient to reduce theLOI at 900*C. to less than about 10wt.%.
 11. The method of claim 10further characterized in that said solution contains sodium fluoride ina concentration less than its solubility limit and sodium hydroxide in aconcentration of from about 0.5 to about 10 wt. %.
 12. The method ofclaim 10 further characterized in that said sodium-exchanged basematerial is essentially completely exchanged with barium and potassiumcations in a weight ratio of from about 1.5 to
 200. 13. The method ofclaim 10 further characterized in that said sodium-exchanged basematerial is completely exchanged with barium cations.
 14. A solidadsorbent prepared by contacting a base material comprising X or Ystructured zeolite with a fluoride containing aqueous sodium hydroxidesolution at first ion exchange conditions to effect the addition ofsodium cations to and the extraction of alumina from said base material,treating the sodium-exchanged base material at second ion exchangeconditions to effect the essentially complete exchange of sodium cationswith barium or barium and potassium cations and drying the thusexchanged base material at conditions to reduce the LOI at 900*C. toless than about 10 wt. %.